(1) Field of the Invention
This invention relates to respiratory apparatus and more particularly to apparatus for controlling the pressure in cuffs of tracheal tubes.
(2) Description of the Prior Art
During controlled ventilation in patients on automatic respirators, a tracheal tube is inserted into the trachea. During the inhalation mode of the respirator, it is necessary to seal the tube with respect to the trachea so that gas passing through the tracheal tube is forced into the lungs of the patient.
To seal the tube with respect to the trachea, the tracheal tube is provided with a pressure cuff which presses against the trachea once the tube is positioned within the trachea. Patients may often require respiratory support for several days or weeks. During lengthy respirator support, it is not unusual for the inner walls of the trachea to become ischemic. The contact between the cuff and the trachea may lead to ulceration, fistulization into an adjacent material branch, and possible stenosis of the tissues lining the inner wall of the trachea. The damage of the inner wall of the trachea is believed to be, at least in part, due to the fact that the pressure of the cuff when fully inflated is sufficient to reduce or terminate blood circulation to the cells in the region of the inner wall of the trachea.
It is well known that the cuff can be inflated during the inhalation mode of the respirator and deflated during the exhalation mode of the respirator. During the exhalation mode, the air in the cuff can be released to deflate the cuff and allow blood to circulate to the cells lining the inner wall of the trachea.
U.S. Pat. No. 3,481,339 discloses an endotracheal tube including a cuff which is said to inflate during the inhalation mode and deflate during the exhalation mode. As disclosed in that patent, the cuff surrounding the endotracheal tube is divided into an external subchamber and an internal subchamber; the internal subchamber being in fluid communication with the interior of the endotracheal tube. During the inhalation mode of the respirator, air or other appropriate gas is forced through the tube and is said to inflate the internal subchamber and press the cuff against the trachea. One drawback with the cuff disclosed in Pat. No. 3,481,339 is that the pressure in the cuff during the inhalation mode can not be controlled and is approximately the same or only slightly greater than the pressure in the trachea. Likewise, the pressure in the cuff during the exhalation mode of the respirator can not be controlled. Another obvious disadvantage of the type of cuff proposed in Pat. No. 3,481,339 is that it is quite difficult to manufacture.
U.S. Pat. No. 3,529,596 discloses an automatic volume limited intermittent cuff inflator-deflator. In the device disclosed in Pat. No. 3,529,596, a pneumatic cylinder with a piston operated by a control line from the respirator inflates and deflates the tracheal cuff in response to the cycle of the respirator. One end of the cylinder is connected via a line to the tracheal cuff. As the piston moves back and forth, the cuff is inflated and deflated. One drawback with the device disclosed in Pat. No. 3,529,596 is that the inflation and deflation of the cuff appears to be relatively slow in response to the cycling of the respirator. Another drawback is that the cuff is inflated to a preset VOLUME, which can cause drastic increases in PRESSURE to result from changes of position, coughing, or other physiological variables which affect tracheal diameter.
U.S. Pat. No. 4,020,849 discloses an apparatus for inflation of cuffs for tracheal tubes. That patent discloses a connector member which connects a tracheal tube to the source of breathing air, the connector member incorporating an auxiliary passage having an entrance device for inflating the cuff with the breathing air. The entrance device responds to raised pressure in the connector to admit the breathing air for filling the cuff and responds to a decrease in pressure to close the auxiliary passage at a desired level for retaining sealing pressure in the cuff. It should be noted that the maximum pressure to which the cuff can be inflated is approximately the maximum pressure of the air from the respirator.
U.S. Pat. No. 3,931,822 discloses an automatic alternating cuff endotracheal tube inflator. That patent discloses an endotracheal tube including at least two cuffs which are alternately inflated. The cuffs of the device of Patent No. 3,931,822 are inflated and deflated by a complicated mechanism which includes a lever arm, an electrical solenoid, and an air bellows.
It is one object of the present invention to provide an apparatus for controlling the pressure within a tracheal cuff and which may be used with various known tracheal cuffs.
It is another object of the invention to provide an apparatus for controlling the pressure within a tracheal cuff and which can be adapted to a conventional respirator.
It is another object of the present invention to provide an apparatus which has a relatively fast response time, that is, the cuff is pressurized quickly when the respirator cycles to the inhalation mode.
It is a further object of the invention to provide an apparatus wherein the pressure of the cuff during the inhalation mode of the respirator may be controlled.
It is another object of the present invention to provide an apparatus wherein the pressure in the cuff during the exhalation mode of the respirator can be controlled.
It is another object of the present invention to provide an apparatus for controlling pressure within tracheal cuffs which will respond to signals from a conventional respirator during conditions of sustained Positive End Expiratory Pressure (PEEP) and Intermittent Mandatory Ventilation (IMV).
It is another object of the present invention to provide an apparatus for controlling the pressure within a tracheal cuff which is pressure-limited, not volume-limited.